Fjords in the Arctic are key ecosystems and of great importance to both natural systems and human societies. The in situ monitoring of these systems is however quite difficult and some variables, such as light availability, are more difficult to collect than others. To address this knowledge gap the 'FjordLight' dataset was published on PANGAEA (Gentili et al., 2023). This dataset provides monthly values for bottom PAR (PAR_B) across seven key Arctic fjords, as well as annual averages and monthly climatology values for PAR_B, surface PAR (PAR(0-)), and the extinction coefficient of photosynthetically available radiation (K_PAR). Thanks to the rapid interest from the community for this dataset, we are now expanding upon it with an addendum: a collection of three additional files for each of the seven sites.Of particular importance to the study of photo-biological processes in the water column is K_PAR; however, the original FjordLight dataset did not include these monthly values because the size of these combined data would make the file large for many users' systems. In the present addendum, all monthly K_PAR data are included. These values are based on estimates of surface turbidity and irradiance derived from remotely sensed observations. Also included in this addendum are one file each for the standard deviation of the monthly climatologies and the annual climatologies for the three PAR variables (e.g. PAR(0-), K_PAR, PAR_B). Note that as these files are in addition to the original FjordLight dataset, they do not contain the same list of global variables and other metadata. All variables in the NetCDF files in this addendum are internally documented. The FjordLight R package that may be utilised to access and work with the FjordLight data has been updated and expanded for reading new files (Gentili et al., 2023; https://cran.r-project.org/web/packages/FjordLight/index.html).

File descriptions:Satellite data collected between 2003 and 2022 (SeaWiFS/ MODIS/ MERIS/ VIIRS) in conjunction with IBCAO gridded bathymetry data (200 m) and Norwegian mapping authority data (50-150 m) are used to estimate the extinction coefficient of light in the water column for of a series of representative EU Arctic fjords, 2003-2022. Also included are the standard deviation (SD) for the monthly and annual climatologies calculated for all variables (e.g. PAR(0-), K_PAR, PAR_B). The data for each of the seven sites are available as three NetCDF files.The monthly K_PAR data are available in the files:_MonthlyKpar.ncThe monthly climatology SD data:ClimSD.ncThe yearly climatology SD data:YearlySD.ncThe sites are:disko.nc = Disko Bay (Greenland)is.nc = Isfjorden (Svalbard)kong_.nc = Kongsforden (Svalbard)nuup_.nc = Nuup Kangerlua (Greenland)por_.nc = Porsangerfjorden (Norway)stor_*.nc = Storfjorden (Sbalbard)young_.nc = Young Sound (Greenland)